function toRadians(d){
  return d*Math.PI/180
}
function getDistance(lat1,lng1,lat2,lng2){
  const R =6378137
  let dis = 0
  let radLat1 = toRadians(lat1)
  let radLat2 = toRadians(lat2)
  let deltaLat = radLat1 - radLat2
  let deltaLng = toRadians(lng1) - toRadians(lng2)
  dis=2*R*Math.asin(Math.sqrt(Math.pow(Math.sin(deltaLat/2),2)
  +Math.cos(radLat1)*Math.cos(radLat2)*Math.pow(Math.sin(deltaLng/2),2)
  ))
  return dis 
}
module.exports={
  getDistance
}